The President-elect of the United States is the apparent winner, as ascertained by the GSA Administrator, following the general election on Election Day in November,[4] and the finalized winner when the votes cast in December by the Electoral College are counted by a joint session of Congress in early January.

During the period between the presidential election and the inauguration, the outgoing president is said to be a lame duck, while the incoming president heads a presidential transition to ensure a smooth handover of power.

If a sitting president has won re-election, the incumbent is not referred to as a president-elect as he or she is already in office and is not waiting to become president. Likewise, if a Vice President succeeds to the Presidency by way of the President's death, resignation or removal (via impeachment) from office, that person never holds the title of President-elect, as they would become President immediately.

Article II, Section 1, Clause 2 of the United States Constitution, along with the Twelfth and Twentieth Amendments govern the election of the U.S. President. The procedure is also regulated by federal and state laws. Under federal Law, the presidential electors (the members of the Electoral College) must be "appointed, in each state, on the Tuesday next after the first Monday in November, in every fourth year". Thus, all states appoint their electors on the same date, in November, once every four years. However, the manner of appointment of the electors is determined by the law of each State.

Currently, in every state, an election by the people is the method employed for the choice of the members of the Electoral College; however, any state remains free to change its manner of appointing its slate of members of the Electoral College, so that the law of a state could, for instance, prescribe election by the state legislature, or even choice by the state's governor, as the manner of appointment of the electors representing the state. In spite of that theoretical possibility, a popular election in each state is the established method of selection of the members of the Electoral College, and given that all the statewide elections happen on the same date, the simultaneous elections resemble a national general election.

On the Monday after the second Wednesday in December, the electors of each state meet in their respective state capitals (and the electors of the District of Columbia meet in the federal capital) and in those meetings the electors cast their votes for President and Vice-President of the United States.

At the conclusion of their meetings, the electors of each state and of the District of Columbia then execute a "certificate of vote" (in several original copies), declaring the vote count in each meeting. To each certificate of vote, a certificate of ascertainment is annexed. Each state's (and the District of Columbia's) certificate of ascertainment is the official document (usually signed by the governor of the state and/or by the state's secretary of state) that declares the names of the electors, certifying their appointment as members of the Electoral College. Given that in all states the electors are currently chosen by popular election, the certificate of ascertainment also declares the results of the popular vote that decided the appointment of the electors. The electors in each state and of the District of Columbia then send the certificates of vote, with the enclosed certificates of ascertainment, to the President of the U.S. Senate.

The electoral votes are counted in a joint session of Congress in early January (on January 6 as required by 3 U.S. Code, Chapter 1 or an alternative date set by statute) and if the ballots are accepted without objections, the candidate winning at least 270 electoral votes (a majority of the total number of votes) is announced the President-elect by the incumbent Vice President, in their capacity as President of the Senate.

No constitutional provision or federal law requires electors to vote according to the results of their states' popular vote, though some states bind their electors to their pledges by state law. Historically, there have been only a few instances of electors not casting their ballots for the candidates to whom they were pledged, and such instances have never resulted in changing the final outcome of a presidential election. Popular vote does not declare the Presidency, Electoral College vote does. Even if popular vote goes to one candidate, another may win the electoral vote and Presidency, as has happened in 1876, 1888 and 2000,[5] and will apparently happen again in the 2016 election.[6]

Two congressional reports found that the president-elect is the eventual winner of the majority of electoral ballots cast in December. The Congressional Research Service (CRS) of the Library of Congress, in its 2004 report "Presidential and Vice Presidential Succession: Overview and Current Legislation,"[7] discussed the question of when candidates who have received a majority of electoral votes become president-elect. The report notes that the constitutional status of the president-elect is disputed:

Some commentators doubt whether an official president- and vice president-elect exist prior to the electoral votes being counted and announced by Congress on January 6, maintaining that this is a problematic contingency lacking clear constitutional or statutory direction. Others assert that once a majority of electoral votes has been cast for one ticket, then the recipients of these votes become the president- and vice president-elect, notwithstanding the fact that the electoral votes are not counted and certified until the following January 6.

The CRS report quotes the 1933 U.S. House committee report accompanying the Twentieth Amendment as endorsing the latter view:

It will be noted that the committee uses the term "president elect" in its generally accepted sense, as meaning the person who has received the majority of electoral votes, or the person who has been chosen by the House of Representatives in the event that the election is thrown into the House. It is immaterial whether or not the votes have been counted, for the person becomes the president-elect as soon as the votes are cast.[8]

Both reports make clear that becoming president-elect is contingent upon winning a majority of the electoral votes cast.

Scholars have noted that the national committees of the Democratic and Republican parties have adopted rules for selecting replacement candidates in the event of a nominee's death, either before or after the general election. If the apparent winner of the general election dies before the Electoral College votes in December the electors probably would endorse whatever new nominee their national party selects as a replacement (although they may be prevented from doing so in many states, because those states have laws requiring electors to vote for the person to which they are pledged, and some states invalidate votes that were cast for anyone else). If the apparent winner dies between the College's December vote and its counting in Congress in January, the Twelfth Amendment stipulates that all electoral ballots cast shall be counted, presumably even those for a dead candidate. The U.S. House committee reporting on the proposed Twentieth Amendment said the "Congress would have 'no discretion' [and] 'would declare that the deceased candidate had received a majority of the votes.'"[9]

In cases where a president has not been chosen by January 20 or the president-elect "fails to qualify," the vice president-elect becomes acting president on January 20 until there is a qualified president. If the president-elect dies before noon January 20, the Twentieth Amendment states the vice president-elect becomes president. In cases where there is no president-elect or vice president-elect, the amendment also gives the Congress the authority to declare an acting president until such time as there is a president or vice president. At this point the Presidential Succession Act of 1947 would apply, with the office of the Presidency going to the speaker of the House of Representatives, followed by the president pro tempore of the Senate and various Cabinet officers.

The closest instance of a vice president-elect becoming president came just 23 days after the ratification of the Twentieth Amendment. On February 15, 1933, Giuseppe Zangara fired a gun at President-elect Franklin D. Roosevelt, but missed, instead hitting Chicago Mayor Anton Cermak. If the assassination attempt on Roosevelt had been successful then, pursuant to Section 3 of the amendment, Vice President-elect John Nance Garner would have been sworn in as president on Inauguration Day (March 4, 1933).

Recent presidents-elect have assembled United States presidential transition teams to prepare for a smooth transfer of power following the inauguration. Outgoing presidents have cooperated with the president-elect on important policy matters during the last two months of the president's term to ensure a smooth transition and continuity of operations that have significant national interests. Before the ratification of the Twentieth Amendment in 1933, which moved the start of the presidential term to January, the president-elect did not assume office until March, four months after the popular election.

The Presidential Transition Act of 1963[4] authorizes the Administrator of the General Services Administration to certify, even before the December vote of the Electoral College, the apparent winner of the November general election as the president-elect for the purposes of receiving federal transition funding, office space and communications services prior to the beginning of the new administration on January 20.[10]

The president-elect assumes office as the next president of the United States upon the expiration of the term of the previous officeholder at noon on January 20. This procedure has been the subject of many misinterpretations and urban legends, such as the myth of David Rice Atchison's one-day-long presidency, which is predicated upon false assumptions and a logical flaw. Taking the formal oath of office does not affect the automatic accession to and occupation of the office of the presidency, which, in the case of the president, proceeds, ipso facto, from the expiration of the predecessor's term and the immediate start of the new four-year term. The oath of office is necessary so that the president can "enter upon the execution" of his office, but he or she is already president from the start of his term.[citation needed]

During the presidential transition period, the President–elect's running mate is known as the Vice President-elect. Here also, in the strictest sense the title applies only to an individual who has been selected by the Electoral College (or by the Senate), though the term is commonly used to describe the individual who has obtained a sufficient number of electors to win the Electoral College vote.

^ ab"Presidential Transition Act of 1963 (Public Law 88-277)". General Services Administration. Retrieved 2016-05-17. The terms "President-elect" and "Vice-President-elect" as used in this Act shall mean such persons as are the apparent successful candidates for the office of the President and Vice President, respectively, as ascertained by the Administrator following the general elections held to determine the electors of the President and Vice-President in accordance with title 3, United States code, sections 1 and 2.

^"U.S. National Archives and Records Administration FAQ". Retrieved 2008-11-23. The Supreme Court has held that the Constitution does not require that electors be completely free to act as they choose and therefore, political parties may extract pledges from electors to vote for the parties' nominees.

^In November 2000, the GSA administrator did not name a president-elect until the legal disputes over vote counting in Florida were resolved. Schrader, Esther (2000-11-28). "GSA Denies Bush Transition Aid, Citing Legal Battle". Los Angeles Times. Retrieved 2008-11-16. It started early Monday, when the Bush team asked for access to the taxpayer-funded transition offices that are to be used by the president-elect. The General Services Administration refused, explaining it was best to wait until the legal challenges in Florida had run their course.

^Date the House and Senate met in joint session to count the electoral votes, and declared Washington elected president